JP2018168413A - Non-oriented electrical steel sheet and manufacturing method thereof, motor core and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density, which is preferable for a split core application, and an excellent magnetic property, and a method for manufacturing the same. SOLUTION: In mass%, C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0.001% to 2.500%, Mn: 0.01% to 3.00. %, P: 0.180% or less, S: 0.0030% or less, and the balance: Fe and an impurity-containing chemical composition in the intermediate layer having a plate thickness of 1/10 to a plate thickness of 1/5 { 223} <252> Non-oriented electrical steel sheet having an degree of integration of 6 or less. [Selection diagram] None

Description

  The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and a motor core and a manufacturing method thereof.

In recent years, especially in the field of electrical equipment such as rotating machines, small and medium-sized transformers, electrical components, etc., the global environment conservation movement represented by global power reduction, energy saving, CO ₂ emission reduction, etc. Therefore, there is an increasing demand for higher efficiency and smaller motors. Under such a social environment, improving the performance of the non-oriented electrical steel sheet used as the core material of the motor is an urgent issue.

For example, in the automobile field, non-oriented electrical steel sheets are used as a core of a drive motor of a hybrid drive vehicle (HEV: Hybrid Electric Vehicle) or the like. Drive motors used in HEVs are increasing in demand for downsizing due to restrictions on installation space and reduced fuel consumption due to weight reduction.
With the demand for miniaturization of drive motors, motors need to have higher torque. Therefore, the non-oriented electrical steel sheet is required to further improve the magnetic flux density.
Moreover, since there is a limit to the capacity of the battery mounted on the automobile, it is necessary to reduce energy loss in the motor. Therefore, further reduction in iron loss is required for non-oriented electrical steel sheets.

Among these motor cores, for example, there is a so-called “divided core” in which a winding is wound around cores divided into one tooth, and then the cores are assembled to finish the final form of the stator core. The non-oriented electrical steel sheet used for the split core is required to have good characteristics in one specific direction or two directions rather than uniform characteristics in the in-plane direction.
As a non-oriented electrical steel sheet corresponding to such characteristics, for example, as disclosed in Patent Documents 1 and 2, the magnetic properties in the rolling direction and the perpendicular direction of rolling in the plate surface of the non-oriented electrical steel sheet are improved. Steel plates have been proposed.

In addition, the split core is often applied to a core having a complicated shape, and the member shape is required to have particularly high accuracy. However, magnetic steel sheets that have been sufficiently heat-treated to reduce the iron loss and coarsened the crystal grains are also soft, so that when the member (steel sheet blank) is punched, the shape accuracy may decrease. It has been pointed out that there is.
On the other hand, for example, Patent Documents 3 to 5 disclose techniques for improving punching accuracy by hardening a steel plate or refining crystal grains.

  In addition, for example, it is known that hot rolling conditions have a great influence on the magnetic properties of the final product. As disclosed in Patent Documents 6 to 9, the lubrication, strain amount, and rolling temperature are precisely controlled. Efforts to control the finishing hot rolling finish temperature to about 800 ° C. or less have been made.

Furthermore, the electromagnetic steel sheet may be used after additional heat treatment. As a typical example, “SRA (Stress Relief Annealing)” is known. This is a heat treatment for finally removing unnecessary strain because the strain inevitably introduced into the steel plate due to punching or the like when processing the steel plate as an electrical component particularly worsens the iron loss. This heat treatment is applied to a member cut out from the steel plate (steel plate blank) or a motor core (for example, a stator core) in which the members are laminated.
However, the strain relief annealing has the effect of releasing the strain and improving the iron loss, but at the same time, the crystal orientation which is not preferable for the magnetic characteristics develops and the magnetic flux density may be lowered. Therefore, when particularly high magnetic characteristics are required, it is required to avoid a decrease in magnetic flux density during strain relief annealing.

Although few techniques have been studied for controlling the magnetic characteristics in the strain relief annealing, a technique related to a semi-processed non-oriented electrical steel sheet is disclosed as a related technique. Semi-processed non-oriented electrical steel sheets are shipped on the premise that the steel sheet after recrystallization by finish annealing is delivered with strain, and then heat treatment is performed by the steel sheet user to release the strain and obtain magnetic properties. Is.
For example, Patent Document 10 shows that it is effective to set the heating rate during finish annealing to 5 ° C./sec to 40 ° C./sec. Patent Document 11 discloses a technique that improves the magnetic characteristics for a semi-process by increasing the heating rate up to 740 ° C. to 100 ° C./sec or more.

JP 2008-127600 A JP 2012-132070 A International Publication No. 2003/002777 JP 2003-197414 A JP 2004-152791 A Japanese Patent Laid-Open No. 11-229096 JP 2001-279326 A JP 2011-111658 A JP 2006-045613 A Japanese Patent Laid-Open No. 03-223424 International Publication No. 2014/129034

  However, with the existing technology, for split cores, the magnetic properties in one or two directions are good, the processing accuracy when punching is good, and the magnetic properties after strain relief annealing It was not enough to consider that it was good. Therefore, further improvement of these characteristics has been demanded for the split core.

  The present invention has been made in view of the above circumstances, and an object of the present invention is excellent in magnetic properties in two directions, ie, a rolling direction and a direction perpendicular to the rolling direction, and punching accuracy for a split core. The present invention provides a non-oriented electrical steel sheet having excellent magnetic properties even after annealing and a method for producing the same.

  The present inventors have studied to obtain a non-oriented electrical steel sheet having excellent magnetic properties by changing the crystal orientation in the thickness direction. Pursuing that condition, reducing the degree of {223} <252> orientation accumulation in the intermediate layer, for the split core, the magnetic properties in the two directions, the rolling direction and the direction perpendicular to the rolling direction, and the punching accuracy, Furthermore, it has been found that it has a strong correlation with the improvement of magnetic properties after strain relief annealing. And the conditions for obtaining the steel plate which has these characteristics were examined in detail. As a result, it was found that a steel sheet having the above characteristics can be obtained when the difference between the surface temperature of the steel sheet and the center thickness of the steel sheet is within a specific range at the start of finish hot rolling.

  Furthermore, from the viewpoint that the texture change in the intermediate layer is related to the shear deformation due to rolling, detailed research was conducted on the state of strain imparted by hot rolling. As a result, in the finishing hot rolling pass schedule in which a plurality of passes are continuously performed, even when the strain applied to the steel plate in the first half of the pass is larger than the strain applied in the second half, the intermediate layer of the steel plate , {223} <252> It was confirmed that the degree of integration of the orientation could be reduced.

  That is, the present invention has been made based on these findings. That is, the gist of the present invention is as follows.

<1> By mass%
C: 0.0030% or less,
Si: 0.01% to 3.50%
Al: 0.001% to 2.500%
Mn: 0.01% to 3.00%,
P: 0.180% or less,
S: 0.0030% or less, and the balance: chemical composition containing Fe and impurities,
A non-oriented electrical steel sheet having a degree of integration of {223} <252> orientations of 6 or less in an intermediate layer having a thickness of 1/10 to 1/5.
<2> The non-oriented electrical steel sheet according to <1>, wherein a degree of integration of {100} <001> orientations in a surface layer from the steel sheet surface to a plate thickness of 1/10 is 6 or more.
<3> In the surface layer, a ratio between an integration degree of {100} <001> orientation (MI ₀₀₁ ) and an integration degree of {100} <011> orientation (MI ₀₁₁ ) is
MI ₀₀₁ / MI ₀₁₁ > 1.0
The non-oriented electrical steel sheet according to <1> or <2> satisfying the relationship:
<4> The ratio (B ₅₀ / Bs) between the average magnetic flux density B ₅₀ and the saturation magnetic flux density Bs in the rolling direction and the direction perpendicular to the rolling direction when excited with a magnetizing force of 5000 A / m is 0.890 or more. The non-oriented electrical steel sheet according to any one of to <3>.
<5> The heat treatment was performed under the conditions that the magnetic flux density of the steel plate before heat treatment was B _A , the heating rate was 100 ° C./hr, the maximum temperature reached 800 ° C., and the holding time at 800 ° C. was 2 hours. when the magnetic flux density of the steel sheet after the _{B B,} the ratio between said _{B a} wherein _{B B is,} to satisfy the relationship of B B / _{B a} ≧ 0.980 <1> ~ or <4> 1 The non-oriented electrical steel sheet according to item.
<6> A hot rolling step of hot rolling a slab having the chemical composition according to <1>,
A cold rolling step for cold rolling to the steel plate after the hot rolling step;
A finish annealing step for finish annealing the steel sheet after the cold rolling step;
The method for producing a non-oriented electrical steel sheet according to any one of <1> to <5>, wherein the hot rolling step satisfies at least one of the following conditions (a) and (b):
(A) Finishing hot rolling is started by setting the difference between the surface temperature Ts of the steel sheet and the center thickness Tc of the sheet to 50 ° C. or more. (B) (Strain amount σ1 applied to the steel sheet in the first half of the pass) / (In the second half of the pass) <7> The non-direction according to any one of <1> to <5>, in which finish rolling is continuously performed in a plurality of passes so as to satisfy the condition of strain amount σ2) ≧ 1.5 applied to the steel plate. Motor core with laminated magnetic steel sheets.
<8><1>-<5> to the non-oriented electrical steel sheet according to any one of the above, a process of punching to obtain a punched member;
Laminating the punched member;
A method for manufacturing a motor core.

  According to the present invention, for split cores, the magnetic properties in two directions, the rolling direction and the direction perpendicular to the rolling direction, and the punching accuracy are excellent, and the magnetic properties are excellent even after performing strain relief annealing. The non-oriented electrical steel sheet and the manufacturing method therefor can be provided.

It is a perspective view which shows an example of the motor core which concerns on this embodiment.

Hereinafter, an example of a preferred embodiment of the present invention will be described in detail.
In addition, in this specification, the numerical range represented using "to" means the range which includes the numerical value described before and behind "to" as a lower limit and an upper limit.

In this specification, when referred to as plate thickness 1/10, plate thickness 1/5, and plate thickness 1/2, a predetermined position in the plate thickness direction from the steel plate surface is indicated.
Moreover, a surface layer shows the area | region from the steel plate surface to board thickness 1/10. An intermediate | middle layer shows the area | region from board thickness 1/10 to board thickness 1/5. The center layer indicates a region from a plate thickness 1/5 to a plate thickness 1/2.

  In this specification, for each direction (for example, {223} <252> direction, {100} <001> direction, etc.), the Miller index in the normal direction of the rolling surface (rolling surface direction), and the rolling direction With respect to the Miller index in the parallel direction (in-rolling surface direction), the direction within ± 5 ° is assumed to be the direction.

<Non-oriented electrical steel sheet>
(Characteristics of crystal orientation)
The non-oriented electrical steel sheet according to the present embodiment is mass%, C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0.001% to 2.500%, Mn: It has a chemical composition containing 0.01% to 3.00%, P: 0.180% or less, S: 0.0030% or less, and the balance: Fe and impurities.

The non-oriented electrical steel sheet according to the present embodiment has an accumulation degree of {223} <252> orientation in the intermediate layer of 6 or less (this is referred to as a feature (A)).
The non-oriented electrical steel sheet according to the present embodiment has the above-described characteristics, so that it has excellent magnetic characteristics in two directions, ie, a rolling direction and a direction perpendicular to the rolling direction, and punching accuracy for the split core, and further, strain relief annealing. Even after application, the magnetic properties are excellent (hereinafter, these properties may be referred to as “divided core properties”). This will be described below.

It is an important feature in the non-oriented electrical steel sheet of the present embodiment that the degree of integration of {223} <252> orientations in the intermediate layer is 6 or less.
The {223} <252> orientation is an orientation that is relatively close to the {111} orientation, which is undesirable for magnetic properties. The {223} <252> azimuth is an azimuth that should be suppressed so as to decrease naturally. Further, the degree of integration of the {223} <252> orientation varies greatly in the intermediate layer of the plate thickness.
Therefore, in the non-oriented electrical steel sheet of the present embodiment, the degree of integration of the {223} <252> orientation in the intermediate layer is defined.
Accumulation of the {223} <252> orientation is related to the shear deformation in the steel plate manufacturing process, particularly in the hot rolling process, and the shear deformation in the hot rolling mainly acts strongly in the intermediate layer. Details will be described later.

The {223} <252> orientation tends to accumulate in high-purity steel having a C amount and N amount of several tens of ppm (mass basis) that are cold-rolled and recrystallized annealed. The {223} <252> orientation is also an intermediate orientation between the {111} <211> orientation and the {112} <110> orientation, which is not preferable for the magnetic properties of the non-oriented electrical steel sheet. The {223} <252> orientation is an orientation in which accumulation is difficult to avoid even in the non-oriented electrical steel sheet according to the present embodiment.
Also, the {223} <252> orientation is not only an unfavorable orientation for the magnetic properties, but is not preferred in consideration of application as a material for a split core. In the non-oriented electrical steel sheet according to the present embodiment, it is assumed that the material for the split core has good magnetic properties in the two directions of the rolling direction and the direction perpendicular to the rolling direction. However, the {223} <252> orientation is not an advantageous direction for improving the characteristics in these two directions. For this reason, if the degree of integration of {223} <252> orientations in the intermediate layer is more than 6, it is difficult to obtain good magnetic properties for the split core. Preferably it is 5 or less, More preferably, it is 4 or less. The lower limit value of the degree of integration of {223} <252> orientations in the intermediate layer is not particularly limited, and examples thereof include 1 or more. Of course, as long as accumulation of the {223} <252> orientation in the intermediate layer can be avoided, the degree of integration of this orientation may be zero.

In addition, the crystal having the {223} <252> orientation of the intermediate layer formed through the shear deformation in the hot rolling process has a crystal orientation different from that of the adjacent surface layer and the central layer, so that the crystal grain size is In the case of coarsening, the crystal grains present in the intermediate layer were likely to grow.
However, the non-oriented electrical steel sheet of the present embodiment has a reduced {223} <252> orientation, which is undesirable for the magnetic properties present in the intermediate layer. As a result, it is considered that even when grains are grown by strain relief annealing, it is possible to suppress a decrease in magnetic properties.

  In the non-oriented electrical steel sheet of the present embodiment, the degree of integration of {100} <001> orientations in the surface layer is preferably 6 or more (this is the feature (B)).

As is well known, increasing the {100} orientation is advantageous for magnetic properties. However, in the method of applying strong processing such as low temperature finishing hot rolling in hot rolling and high cold rolling reduction in cold rolling that have been proposed in the past, the {100} orientation increases, but the main orientation is a steel plate. This is the {100} <011> orientation that improves the magnetic properties in the 45 ° direction, and is not necessarily optimal for split core applications.
In the non-oriented electrical steel sheet according to the present embodiment, the {223} <252> orientation that tends to develop during grain growth is suppressed as described above, and as a result, the {100} orientation develops. However, the {100} <001> orientation develops instead of the {100} <011> orientation. This improves the magnetic properties in the rolling direction and the direction perpendicular to the rolling direction of the steel sheet, and exhibits in-plane anisotropy that is preferable for split core applications.

The development of the {100} <001> orientation is considered to be related to the suppression of the {223} <252> orientation described above, and the change of the {100} <001> orientation is particularly remarkable in the surface layer. The reason is unknown, but is presumed as follows.
Conventionally, the {100} <001> orientation of the surface layer was engulfed with the grain growth of {223} <252> orientation in the intermediate layer. On the other hand, in the non-oriented electrical steel sheet according to the present embodiment, accumulation of the {223} <252> orientation of the intermediate layer is suppressed, and therefore the {100} <001> orientation of the surface layer is easily developed. It is thought that.
For this reason, in the non-oriented electrical steel sheet according to this embodiment, the degree of integration of {100} <001> orientations in the surface layer is preferably 6 or more. Preferably it is 9 or more, More preferably, it is 12 or more. In addition, although the upper limit of the integration degree of {100} <001> orientation in a surface layer is not specifically limited, For example, it is mentioned that it is 40 or less.
The crystal orientation selectivity in this grain growth becomes particularly prominent when additional heat treatment is performed at a low heating rate, and is associated with the ability to suppress a decrease in magnetic flux density associated with the growth of recrystallized grains. Conceivable. Details will be described later.

In addition to the above characteristics, the non-oriented electrical steel sheet of the present embodiment has a {100} <001> orientation integration degree (MI ₀₀₁ ) and a {100} <011> orientation integration degree ( the ratio of the MI _{011) is,} it is a good (characterized by, (C) satisfies the relationship _{MI 001 / MI 011> 1.0)} .

The feature (C) is a feature characterized by changing the in-plane orientation of the feature (B). As described above, in the non-oriented electrical steel sheet of the present embodiment, the accumulation in the {223} <252> orientation is reduced in the intermediate layer. Along with this, the accumulation in the {100} direction increases. At this time, the development of the {100} <001> orientation is promoted instead of the {100} <011> orientation. In the non-oriented electrical steel sheet according to the present embodiment, this feature is obtained particularly in the surface layer where the tendency becomes remarkable, in the degree of integration of {100} <001> orientation (MI ₀₀₁ ) and {100} <011> orientation. _Expressed as a ratio to the degree of integration (MI ₀₁₁ ).
It becomes possible to obtain a steel sheet having in-plane anisotropy that is preferable for use as a split core because the texture change in the plane of the {100} orientation is the above relationship. Preferably, MI ₀₀₁ / MI ₀₁₁ is 2.0 or more, more preferably 4.0 or more, and still more preferably 8.0 or more.

The crystal orientation can be measured by the following method. A steel plate sample of about 30 mm × 30 mm cut out from the steel plate is subjected to mechanical polishing and chemical polishing to remove the surface layer on one side. At the time of removing the surface layer, a test piece for measurement with a reduced thickness is prepared until the surface layer of the original steel plate or the center of the intermediate layer in the thickness direction is the surface.
With respect to each measurement specimen, pole figures of {200} plane, {110} plane, and {211} plane are measured by an X-ray diffractometer, and a crystal orientation distribution function ODF (Orientation Determination Function) in each layer is created. Based on this crystal orientation distribution function, the degree of integration of each orientation in each layer is obtained.

  Next, the reason for limiting the chemical composition in the non-oriented electrical steel sheet according to this embodiment will be described. In addition, about the component composition of a steel plate, "%" is "mass%".

  The non-oriented electrical steel sheet according to the present embodiment is mass%, C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0.001% to 2.500%, Mn: It has a chemical composition consisting of 0.01% to 3.00%, P: 0.180% or less, S: 0.0030% or less, and the balance: Fe and impurities.

(C: 0.0030% or less)
C is a component that increases iron loss and causes magnetic aging, so the lower the content of C, the better. Therefore, the C content is 0.0030% or less. The upper limit with preferable C amount is 0.0025% or less, More preferably, it is 0.0020% or less. Although the lower limit of the C content is not particularly limited, the C content is practically 0.0001% or more in view of industrial purification technology, and 0.0005% or more in consideration of the manufacturing cost.

(Si: 0.01% to 3.50%)
As the content of Si increases, the magnetic flux density decreases and the hardness increases, thereby deteriorating the punching workability. Moreover, also in the manufacturing process of the non-oriented electrical steel sheet itself, workability such as cold rolling is reduced and the cost is increased. Therefore, the upper limit of the Si content is 3.50% or less. A preferable upper limit of the amount of Si is 3.20% or less, and a more preferable upper limit is 3.00% or less. On the other hand, Si has the effect of increasing the electrical resistance of the steel sheet to reduce eddy current loss and reduce iron loss. Therefore, the lower limit of Si content is 0.01% or more. The preferable lower limit of the Si amount is preferably 0.10% or more, more preferably 0.50% or more, and further preferably 1.00% or more.

(Al: 0.001% to 2.500%)
Al is inevitably contained from ores and refractories, and is also used for deoxidation. Considering this, the lower limit is made 0.001% or more. Further, Al, like Si, is a component having an action of reducing iron loss by increasing electric resistance and reducing eddy current loss. Therefore, Al may be contained in an amount of 0.200% or more. On the other hand, when the Al content is increased, the saturation magnetic flux density is lowered and the magnetic flux density is lowered. Therefore, the upper limit of the Al content is 2.500% or less. Preferably it is 2.000% or less.

(Mn: 0.01% to 3.00%)
Mn increases electrical resistance to reduce eddy current loss and suppresses precipitation of fine sulfides such as MnS that are harmful to crystal grain growth. For these purposes, Mn is contained in an amount of 0.01% or more. A preferable lower limit of the amount of Mn is 0.15% or more. However, when the content of Mn increases, the crystal grain growth property during annealing decreases, and the iron loss increases. Therefore, the upper limit of the Mn content is 3.0% or less. The upper limit with the preferable amount of Mn is 2.50% or less, More preferably, it is 2.00% or less.

(P: 0.180% or less)
P has the effect of increasing the strength without reducing the magnetic flux density. However, when P contains excessively, the toughness of steel will be impaired and it will become easy to produce a fracture | rupture in a steel plate. Therefore, the upper limit of the P amount is 0.180%. In terms of suppressing the breakage of the steel sheet, it is better that the amount of P is small. The upper limit with preferable P amount is 0.150% or less, More preferably, it is 0.120% or less, More preferably, it is 0.080% or less. The lower limit of the amount of P is not particularly limited, but it is 0.001% or more in consideration of manufacturing cost.

(S: 0.0030% or less)
Since S hinders recrystallization and crystal grain growth during finish annealing due to fine precipitation of sulfides such as MnS, it is set to 0.0030% or less. The upper limit with preferable S content is 0.0020% or less, More preferably, it is 0.0015% or less. The lower limit of the S content is not particularly limited. However, considering industrial purification technology, the S content is practically 0.0001% or more, and considering the manufacturing cost, it is 0.0005% or more.

(Fe and impurity elements)
The balance of the steel sheet is Fe and impurity elements. Here, the impurity element refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally included in the steel plate.

The said chemical composition is a composition of the steel which comprises a steel plate. When the steel plate used as a measurement sample has an insulating film or the like on the surface, the measurement is performed after removing this.
Examples of a method for removing the insulating film of the non-oriented electrical steel sheet include the following methods.
First, a non-oriented electrical steel sheet having an insulating film or the like is immersed in an aqueous sodium hydroxide solution (NaOH: 10% by mass + H ₂ O: 90% by mass) at 80 ° C. for 15 minutes. Subsequently, it is immersed in an aqueous sulfuric acid solution (H ₂ SO ₄ : 10% by mass + H ₂ O: 90% by mass) at 80 ° C. for 3 minutes. Thereafter, the substrate is immersed and washed with an aqueous nitric acid solution (HNO ₃ : 10% by mass + H ₂ O: 90% by mass) at room temperature (25 ° C.) for 1 minute. Finally, dry with a warm air blower for 1 minute. Thereby, the steel plate from which the below-mentioned insulating film was removed can be obtained.

  The content ratio of each element in the steel sheet can be measured by, for example, inductively coupled plasma mass spectrometry (ICP-MS method: Inductively Coupled Plasma-Mass Spectrometry). Specifically, first, a non-oriented electrical steel sheet to be measured is prepared. A part of the electromagnetic steel sheet is cut into a face shape and weighed, and this is used as a measurement sample. The measurement sample is dissolved in an acid to obtain an acid solution, and the residue is recovered by filter paper and separately melted in alkali or the like, and the melt is extracted with an acid to form a solution. An ICP-MS measurement solution can be obtained by mixing the solution and the acid solution and diluting the solution as necessary.

(Magnetic properties of non-oriented electrical steel sheet)
The non-oriented electrical steel sheet according to the present embodiment has excellent magnetic properties in two directions, ie, a rolling direction and a direction perpendicular to the rolling direction, for the split core, and when excited with a magnetizing force of 5000 A / m, The ratio (B ₅₀ / Bs) between the average magnetic flux density B _{50 in} the perpendicular direction and the saturation magnetic flux density Bs is preferably 0.890 or more. Preferably it is 0.900 or more, More preferably, it is 0.905 or more, More preferably, it is 0.910 or more. Although an upper limit is not specifically limited, It is so good that it is close to 1, for example, 0.980 or less is mentioned.

−Punching accuracy−
As described above, the non-oriented electrical steel sheet according to the present embodiment has a lower degree of integration of the intermediate layer {223} <252> orientation than a normal steel sheet. Thereby, the characteristic preferable also for the punching precision of a non-oriented electrical steel sheet is exhibited. The reason for this is not clear, but it is thought as follows.
Since the {223} orientation close to the {111} orientation is large in work hardening, the plastic deformation region extends from the fracture surface to the inside of the steel material during punching, and the region in which the steel material is stretched and deformed becomes large. For this reason, it is thought that a steel plate with a high integration degree of {223} orientation tends to fall in processing accuracy. Therefore, in order to increase the punching accuracy, it is considered that reducing the degree of integration of {223} <225> orientations works effectively.

-Changes in magnetic properties due to additional heat treatment (strain relief annealing)-
The non-oriented electrical steel sheet according to this embodiment reduces the magnetic flux density that has occurred during the growth of recrystallized grains, even when additional heat treatment (strain relief annealing) is performed at a low heating rate. It can be suppressed.
After the heat treatment is performed under the conditions that the magnetic flux density of the steel plate before additional heat treatment is B _A , the heating rate is 100 ° C./hr, the maximum temperature is 800 ° C., and the holding time is 800 ° C. When the magnetic flux density of the steel sheet is B _B , the ratio of B _B to B _A is B _B / B _A ≧ 0.980 (preferably B _B / B _A ≧ 0.985, more preferably B _B / B _A ≧ 0.990) can be satisfied.
In addition, although the upper limit of B _B / B _A is not particularly defined, the fact that there is no characteristic deterioration due to the additional heat treatment (that is, B _B / B _A = 1.00) is also a target standard. However, in the non-oriented electrical steel sheet of the present embodiment, the crystal orientation is preferably controlled in consideration of the change in the thickness direction, so that a preferred orientation for magnetic properties grows preferentially, and B _B / B _A is It may exceed 1.00.
Here, the method of measuring the magnetic flux densities B _A and B _B before and after the additional heat treatment is performed is the same as B ₅₀ described above.

  In addition, the conditions of the additional heat processing which prescribes | regulates the non-oriented electrical steel sheet which concerns on this embodiment are made into the specific value in a heating rate, the highest attained temperature, and holding time as mentioned above. This is a value that is considered to be representative as a condition for strain relief annealing that is currently practiced practically. When the non-oriented electrical steel sheet according to the present embodiment is used for an application for additional heat treatment, the effect of suppressing the decrease in magnetic flux density due to the additional heat treatment is limited to this value in the heating rate, the maximum temperature reached, and the holding time. It can be enjoyed within a certain range. For example, additional heat treatment conditions for confirming the properties for the split core include a heating rate of 30 ° C./hr to 500 ° C./hr, a maximum temperature of 750 ° C. to 850 ° C., and a holding time at 750 ° C. or higher of 0.5 hours. The range made to -100 hours is mentioned.

  Thus, even if it is a case where the steel plate which concerns on this embodiment is an additional heat processing (strain relief annealing), the fall of a magnetic flux density is suppressed rather than when the stress relief annealing of the conventional steel plate is carried out. Although this reason is not necessarily clear, it thinks as follows.

  In a conventional non-oriented electrical steel sheet, when grain growth at a relatively low temperature is performed by additional heat treatment at a low heating rate such as strain relief annealing, crystal grains having {100} orientation, which is advantageous for magnetic properties, are obtained. The growth of crystal grains having other orientations (for example, {111}, {223}, {112}, etc.) is dominant. Since these orientations grow in particular by phagocytosing the {100} orientation, the magnetic flux density of the conventional non-oriented electrical steel sheet is greatly reduced.

  On the other hand, in the non-oriented electrical steel sheet according to the present embodiment, at least one of the temperature condition of the finish rolling in hot rolling and the pass schedule is controlled under a specific condition. As a result, the non-oriented electrical steel sheet is manufactured (that is, after finish annealing), the {223} <252> orientation accumulation degree in the intermediate layer is reduced, and the {100} <001> orientation is particularly obtained in the surface layer. Development is promoted. For this reason, in the orientation development in the grain growth by the additional heat treatment by the gradual heating after the finish annealing, the growth in the orientation such as {111} is not dominant. Then, the high magnetic flux density in the rolling direction and its perpendicular direction can be obtained without erosion of crystal grains having an orientation (that is, {100} <001> orientation) advantageous for increasing the magnetic flux density in the rolling direction and its perpendicular direction. Presumed to hold.

The effect on the selectivity of the grown grains by such additional heat treatment is that a relatively high heating rate (for example, 10 ° C. per second) is used until the initial stage of grain growth (for example, the grain size is 80 μm or less). (At about 10 ° C./sec or more), a relatively low heating rate and low temperature for a long time (for example, 1 The growth was allowed to proceed at a temperature of about 100 ° C. (100 ° C./hr) or less per hour and a relatively low temperature range of 550 ° C. to 750 ° C. for 2 hours or more as the temperature range where grain growth occurs. The case becomes noticeable.
In the above, the effect of preferable selection of the crystal orientation in the grain growth has been explained by the orientation change at around 80 μm. This effect is, for example, in finish annealing (in rapid heating annealing), more than 80 μm, for example, 100 μm or more. Even in the case of a steel sheet, preferable grain selectivity from the grain growth, for example, 200 μm or more is not lost.
On the other hand, for example, in finish annealing (in rapid heating annealing), a steel sheet having a grain size of less than 20 μm, for example, an unrecrystallized structure remains, is grown to the progress of recrystallization and grain growth from there, for example, about 50 μm. In some cases, the preferred orientation selectivity is not lost.

  The thickness of the non-oriented electrical steel sheet according to the present embodiment may be appropriately adjusted according to the application and the like, and is not particularly limited, but is 0.10 mm to 0.50 mm from the viewpoint of manufacturing. And is preferably 0.15 mm to 0.50 mm. In particular, from the viewpoint of a balance between magnetic properties and productivity, 0.15 mm to 0.35 mm is preferable.

Moreover, the non-oriented electrical steel sheet according to the present embodiment may have an insulating film on the steel sheet surface. The insulating film formed on the surface of the non-oriented electrical steel sheet according to the present embodiment is not particularly limited, and may be selected from known ones according to the application. For example, the insulating film may be either an organic film or an inorganic film. Examples of organic coatings include polyamine resins, acrylic resins, acrylic styrene resins, alkyd resins, polyester resins, silicone resins, fluororesins, polyolefin resins, styrene resins, vinyl acetate resins, epoxy resins, phenol resins, urethane resins, and melamines. Examples thereof include resins. In addition, examples of the inorganic coating include a phosphate coating; an aluminum phosphate coating. Furthermore, the organic-inorganic composite type | system | group film | membrane containing the said resin is mentioned.
Although the thickness of the said insulating film is not specifically limited, It is preferable that it is 0.05-2 micrometers as a film thickness per single side | surface.

<Method for producing non-oriented electrical steel sheet>
As described above, the non-oriented electrical steel sheet according to the present embodiment can be obtained by controlling the temperature condition and pass schedule of finish rolling in hot rolling under specific conditions. The following method is mentioned as an example of the preferable manufacturing method of the non-oriented electrical steel sheet which concerns on this embodiment.
Hereinafter, an example of the preferable manufacturing method of the non-oriented electrical steel sheet according to the present embodiment will be described.

An example of a suitable method for producing the non-oriented electrical steel sheet of the present embodiment is the above-described chemical composition (mass%, C: 0.0030% or less, Si: 0.01% to 3.50%, Al: 0). .001% to 2.500%, Mn: 0.01% to 3.00%, P: 0.180% or less, S: 0.0030% or less, and the balance: Fe and impurities) Hot rolling process (hot rolling) for hot rolling (hot rolling), cold rolling process (cold rolling) for cold rolling (cold rolling) on the steel sheet after hot rolling, and after the cold rolling process And a final annealing step of performing final annealing on the steel sheet.
In the hot rolling process, at least one of the following conditions (a) and (b) is satisfied.
(A) Finishing hot rolling is started by setting the difference between the surface temperature Ts of the steel sheet and the center thickness Tc of the sheet to 50 ° C. or more. (B) (Strain amount σ1 applied to the steel sheet in the first half of the pass) / (In the second half of the pass) The finish rolling is continuously performed for a plurality of passes so as to satisfy the condition of the strain amount σ2) ≧ 1.5 applied to the steel plate.

  Here, (a) and (b) are conditions for controlling the deformation state of the intermediate layer of the steel sheet. By satisfying at least one of these two conditions, preferably both, a steel sheet having an accumulation degree of {223} <252> orientation in the surface layer of 6 or less after finish annealing is obtained (that is, The above-mentioned feature (A) is obtained). And it becomes possible to acquire the characteristic for division | segmentation cores.

  In addition, the non-oriented electrical steel sheet obtained by the above manufacturing method can be a steel sheet having an accumulation degree of {100} <001> orientation in the surface layer of 6 or more (that is, the above-described feature (B) is further obtained). ).

Then, according to the above manufacturing method, the ratio of the integration degree of {100} <001> orientation (MI ₀₀₁ ) and the integration degree of {100} <011> orientation (MI ₀₁₁ ) in the surface layer is MI ₀₀₁ / MI _A steel plate satisfying the relationship of ₀₁₁ > 1.0 is obtained (that is, the above-mentioned feature (C) is further obtained).

  Hereinafter, each process in an example of a preferable manufacturing method is demonstrated.

(Hot rolling process)
The heating temperature of the slab before hot rolling is not particularly limited, but is preferably set to 1000 ° C to 1300 ° C from the viewpoint of cost and the like.

After subjecting the heated slab to rough hot rolling, finish rolling (hereinafter sometimes referred to as “finish hot rolling”) is performed. When the rough rolling is finished and finishing hot rolling is started, the thickness of the steel sheet is 20 mm to 100 mm.
The temperature condition of finish hot rolling and at least one of the conditions of the pass schedule are as follows: the degree of integration of {223} <252> orientation in the intermediate layer of the steel sheet that has been cold-rolled and recrystallized by finish annealing after hot rolling. It can be an effective control factor to suppress.

What is important as the temperature condition for the finish hot rolling is to start rolling in a state where a large difference is provided between the surface temperature Ts of the steel sheet and the center thickness Tc of the sheet thickness. In the present embodiment, the difference between the surface temperature Ts and the sheet thickness center temperature Tc, Ts-Tc is set to 30 ° C. or more, and finishing hot rolling is started, so that in the intermediate layer of the steel sheet after cold rolling and finish annealing { 223} <252> orientation development can be suppressed. Preferably it is 60 degreeC or more, More preferably, it is 100 degreeC or more. In addition, although the upper limit of Ts-Tc is not specifically limited, For example, it is 200 degrees C or less from points, such as productivity.
Here, in this specification, “surface temperature Ts” means a temperature measured by a contact-type thermometer or a radiation thermometer. In the present specification, “plate thickness center temperature Tc” means a temperature obtained by a heat conduction analysis by a generally known difference method.

  In the hot rolling step, examples of a method for forming a temperature difference between the surface temperature Ts and the plate thickness center temperature Tc include the following methods.

  The slab cooled to a surface temperature of, for example, 1000 ° C. or less is charged into a heating furnace having an ambient temperature of 1000 ° C. or more, and the heating furnace is heated before the entire slab is warmed (for example, within 30 minutes after charging). Rough rolling is performed on the slab unloaded from the factory. Although the surface temperature of the steel sheet is reduced by rough rolling, if a sufficient temperature difference is formed between the surface temperature and the sheet thickness center temperature at the time of heating the slab, even at the end of rough rolling, that is, at the start of finish hot rolling. The difference between the surface temperature and the plate thickness center temperature can be secured.

Under the above conditions, the reason why the accumulation of {223} <252> orientations can be suppressed is not clear, but is presumed as follows.
Generally, since the steel sheet becomes soft as the temperature increases, rolling is performed in a state where the surface temperature of the steel sheet is relatively higher than the plate thickness center temperature as in the method of manufacturing the non-oriented electrical steel sheet according to the present embodiment. In this case, the surface layer and the intermediate layer are considered to be more easily deformed than the center layer of the steel plate. For this reason, it is considered that shear deformation in the intermediate layer was suppressed, and the nucleation of the {223} <252> orientation that should appear originally was suppressed.
The reason why the temperature of the steel sheet is defined by the difference from the surface temperature rather than the difference from the temperature of the intermediate layer is in consideration of ease of measurement.

  The finish hot rolling conditions are as follows: (the amount of strain σ1 applied to the steel sheet in the first half of the pass) / (second half of the pass) It is also important to set a pass schedule that satisfies the relationship of strain amount σ2) ≧ 1.5 applied to the steel sheet. (Σ1) / (σ2) is preferably 1.8 or more, more preferably 2.0 or more, and further preferably 2.5 or more.

If it is the continuous hot rolling equipment currently employed in many steel plate manufacturing processes, rolling of 4 to 7 passes is continuously performed at intervals of several seconds or less.
Here, in the method for manufacturing a non-oriented electrical steel sheet according to the present embodiment, “the strain amount σ1 applied to the steel sheet in the first half of the pass” is a case where n is a natural number of 1 or more and the total number of passes is an even number. Is 2n and the odd number is 2n + 1, it means the true strain applied to the steel sheet from the first pass entry side to the n pass exit side.
Similarly, “the amount of strain σ2 applied to the steel plate in the second half of the pass” means that n is a natural number of 1 or more, and when the total number of passes is an even number 2n, the final pass (2n) is output from the entry side of the (n + 1) th pass. It means the true strain applied to the steel plate up to the side. In addition, when the total number of passes is an odd number 2n + 1, it means the true strain applied to the steel sheet from the entry side of the n + 2 pass to the exit side of the final pass (2n + 1).
That is, when the total number of finish rolling passes is 4, the strain amount σ1 applied to the steel plate in the first half of the pass is the true strain applied to the steel plate from the entrance side of the first pass to the exit side of the 2 passes. The amount of strain applied to the steel plate in the second half of the pass represents the true strain applied to the steel plate from the entry side of the third pass to the exit side of the four passes.
Similarly, when the total number of passes of finish rolling is 7, the strain amount σ2 applied to the steel plate in the first half of the pass is the true amount applied to the steel plate from the entrance side of the first pass to the exit side of the 3 passes. It is a strain, and the amount of strain applied to the steel plate in the second half of the pass represents the true strain applied to the steel plate from the entry side of the fifth pass to the exit side of the seventh pass.

  The true strain is obtained by measuring the plate thickness after each pass with a laser measuring instrument and taking the logarithm of the plate thickness ratio before and after the pass.

Under the above conditions, the reason why the accumulation of {223} <252> orientations can be suppressed is not clear, but is presumed as follows.
There are two aspects of setting (strain amount σ1 applied to the steel plate in the first half of the pass) / (strain amount σ2 applied to the steel plate in the second half of the pass) ≧ 1.5. One is the aspect of relatively increasing the amount of distortion in the first half of the pass. The other is the aspect of relatively reducing the amount of distortion in the second half of the pass.
From the viewpoint of relatively increasing the amount of strain in the first half of the pass, when the amount of strain applied in the first half of finish rolling is large, the effect of suppressing the {223} <252> orientation in the intermediate layer is greatly affected. Conceivable. In particular, in the first half of the pass, the plate thickness is thick and it is easy to maintain the temperature difference in the plate thickness direction. Therefore, it is considered that the effect of suppressing the {223} <252> orientation in the intermediate layer is more significant when the above-described Ts−Tc value is large and the amount of strain applied in the first half of finish rolling is large.
On the other hand, from the viewpoint of relatively reducing the strain amount in the second half of the pass, the strain amount applied in the second half of the finish rolling, in which the plate thickness is thin and the temperature difference in the plate thickness direction is difficult to maintain, is { 223} <252> This means that the advantage of utilizing for controlling the orientation is small.

  Moreover, it is good for the temperature of finishing hot rolling to be the temperature range of 500 to 850 degreeC. From the viewpoint of rollability, the preferable lower limit of the finish hot rolling temperature is 550 ° C or higher, more preferably 600 ° C or higher, and further preferably 650 ° C or higher. The upper limit of the finish hot rolling temperature is preferably 800 ° C. or lower, more preferably 750 ° C. or lower, and further preferably 700 ° C. or lower. This is not a novel condition in that the {100} orientation is increased by controlling the hot rolling conditions. However, in the method of manufacturing a non-oriented electrical steel sheet according to the present embodiment, when rolling with the sheet thickness center temperature of the steel sheet being lower than the surface temperature as described above, it can be said that the condition is easily achieved as a result. . And in the non-oriented electrical steel sheet according to the present embodiment, {100} <001 which improves the magnetic properties in two directions of the rolling direction and the direction perpendicular to the rolling, which is preferable for the steel sheet for the split core, among the {100} orientations. > Direction is easy to develop. For this reason, it can be said that it is preferable to control the temperature of finish hot rolling in the temperature range of the said range.

  As described above, it is not necessarily necessary that the change in the deformation state in hot rolling becomes favorable for a specific magnetic property after cold rolling and finish annealing, but at least as described above in hot rolling. It is natural to consider that controlling shear deformation affects the crystal orientation that occurs after cold rolling and finish annealing. The change in crystal orientation from hot rolling to cold rolling to annealing is expected to be elucidated in the future.

(Cold rolling process)
Next, the steel sheet after hot rolling is cold rolled. The rolling reduction of cold rolling is not particularly limited. As a general condition, cold rolling is performed on the steel sheet after hot rolling so that the total rolling reduction in the cold rolling process (total rolling reduction of cold rolling) is 80% or more (preferably 85% or more). It is good. In particular, if a thin electrical steel sheet is used, the total rolling reduction can be 90% or more. The upper limit of the total rolling reduction of cold rolling is preferably 95% or less in consideration of production management such as the capability of the rolling mill and sheet thickness accuracy.

(Finish annealing process)
Next, finish annealing is performed on the steel sheet after cold rolling. The heating conditions in the finish annealing step are not particularly limited.
The soaking temperature of the finish annealing is preferably in the range of 800 ° C. to 1200 ° C. when the iron loss is sufficiently low with the finish annealing. The lower limit temperature of soaking may be a temperature equal to or higher than the recrystallization temperature, but by setting the temperature to 800 ° C. or higher, sufficient grain growth can be caused and the iron loss can be reduced. In this respect, the temperature is preferably 850 ° C. or higher.
In addition, if an additional heat treatment by slow heating such as strain relief annealing is finally performed to grow the crystal grains, the iron loss after the additional heat treatment can be lowered, so the soaking temperature of the finish annealing can be set from the viewpoint of grain growth. Even if it is less than 800 ° C., which is not sufficient, there is no problem. In this case, the effect of avoiding that the magnetic flux density becomes inferior due to the additional heat treatment is remarkably exhibited. In this case, even if an unrecrystallized structure remains in part, it is possible to have a characteristic crystal orientation of the non-oriented electrical steel sheet according to the present embodiment, and the lower limit temperature is, for example, 640 ° C. The above is mentioned. A steel sheet having a fine crystal structure or a partially non-recrystallized structure by lowering the finish annealing temperature has high strength, and is also useful as a high-strength non-oriented electrical steel sheet.
On the other hand, the upper limit of the soaking temperature is preferably set to 1200 ° C. or less in consideration of the load of the annealing furnace, and is preferably 1050 ° C.

  The soaking time may be a time that takes into account the particle size, iron loss, magnetic flux density, strength, and the like. On the other hand, if it is 120 sec or less, crystal grain growth becomes moderate. Therefore, the soaking time is preferably 5 to 120 seconds. Within this range, for example, when an additional heat treatment by subsequent slow heating is performed to cause grain growth, a crystal orientation that can prevent the magnetic properties from becoming inferior is likely to remain.

  In order to obtain the non-oriented electrical steel sheet according to the present embodiment, in addition to the above processes, other processes similar to the manufacturing process of the conventional non-oriented electrical steel sheet may be provided. The other conditions may be the same as those in the conventional non-oriented electrical steel sheet manufacturing process. Specifically, you may have the insulating film formation process which provides an insulating film on the surface of the steel plate (non-oriented electrical steel plate) after a finish annealing process, for example.

  The method of forming the insulating film is not particularly limited. For example, an insulating film forming composition prepared by dissolving the above-described resin or inorganic substance in a solvent is prepared, and the insulating film forming composition is uniformly applied to the steel sheet surface by a known method. An insulating film can be formed by applying to.

  The non-oriented electrical steel sheet according to the present embodiment is obtained by the manufacturing method having the above steps.

According to this embodiment, a non-oriented electrical steel sheet having excellent magnetic properties can be obtained. Therefore, the non-oriented electrical steel sheet according to the present embodiment can be suitably applied as various core materials for electrical equipment, in particular, as core materials for motors such as rotating machines, small and medium-sized transformers, and electrical components.
Hereinafter, the case where the non-oriented electrical steel sheet according to the present embodiment is applied as a motor core will be described.

<Motor core and manufacturing method thereof>
As for the motor core which concerns on this embodiment, the form which laminated | stacked the non-oriented electrical steel sheet which concerns on this embodiment is mentioned. Specifically, the motor core which punched the non-oriented electrical steel plate which concerns on this embodiment, created the punching member (steel plate blank), and laminated and integrated this punching member is mentioned. For example, the motor core according to the present embodiment includes the motor core shown in FIG. 1 as an example.

  FIG. 1 is a schematic diagram illustrating an example of a split core. As shown in FIG. 1, the motor core 100 is formed as a laminated body 13 in which the punching members 11 for the eight divided cores are connected in an annular shape, and the punching members 11 connected in an annular shape are stacked and integrated into eight layers. Is formed. The punching member 11 for the split core is formed by punching a non-oriented electrical steel sheet, a yoke part 17 on an arc, and a teeth part 15 protruding radially inward from the inner peripheral surface of the yoke part 17. It has. The motor core 100 is not limited to the shape, the number, the number of layers, and the like of the punching member 11 forming the motor core 100 shown in FIG.

  The motor core shown in FIG. 1 has been described above, but the motor core according to the present embodiment is not limited to this.

Next, a method for manufacturing a motor core will be described.
The manufacturing method of the motor core according to the present embodiment is not particularly limited, and may be manufactured by a manufacturing method that is usually employed industrially.
Hereinafter, an example of a preferable manufacturing method of the motor core according to the present embodiment will be described.
An example of a preferable manufacturing method of the motor core according to the present embodiment includes a punching process for punching the non-oriented electrical steel sheet according to the present embodiment to obtain a punched member, and a stacking process for stacking the punched members. .

(Punching process)
First, the non-oriented electrical steel sheet of the present embodiment is punched into a predetermined shape having a tooth portion and a yoke portion according to the purpose, and a predetermined number of punched members are manufactured according to the number of stacked layers. The method of punching a non-oriented electrical steel sheet to create a punched member is not particularly limited, and any conventionally known method may be employed.
The punching member may form an uneven portion for stacking and fixing the punching member when punching into a predetermined shape.

(Lamination process)
A motor core is obtained by laminating the punched members created in the punching process. Specifically, a predetermined number of divided core punching members having teeth and yokes are combined in a circular shape and stacked.
The method for fixing the stacked punched members is not particularly limited, and any conventionally known method may be employed. For example, a known adhesive may be applied to the punched member to form an adhesive layer, which may be fixed via the adhesive layer. Moreover, the uneven | corrugated | grooved part formed in each punching member may be mechanically fitted and fixed by applying caulking.

  The motor core according to the present embodiment is obtained through the above steps. Since the motor core according to the present embodiment is manufactured using the non-oriented electrical steel sheet according to the present embodiment, it has a low iron loss and a high magnetic flux density.

  In addition, another example of a preferable manufacturing method of the motor core according to the present embodiment includes a punching process for punching the non-oriented electrical steel sheet according to the present embodiment to obtain a punched member, and a stacking process for stacking the punched members. And after the punching step and before or after the lamination step, the heating rate is 30 ° C./hr to 500 ° C./hr, the maximum temperature is 750 ° C. to 850 ° C., and 750 ° C. And a heat treatment step for heat treatment under the conditions of the above holding time of 0.5 hour to 100 hours.

  That is, the motor core according to the present embodiment has a retention time at specific conditions (heating rate: 30 ° C./hr to 500 ° C./hr, maximum temperature: 750 ° C. to 850 ° C., 750 ° C. or higher after the punching members are stacked. : 0.5 hour to 100 hours) may be subjected to heat treatment (strain relief annealing). Further, in this heat treatment, the punching member before the punching member is laminated may be subjected to the heat treatment under the specific conditions.

  Since the motor core itself is not as thin as a steel plate, the motor core is generally subjected to heat treatment in a finish annealing step in a steel plate manufacturing process that is performed at a heating rate of about several tens of degrees centigrade / sec. In contrast, it has to be very slow, about several hundred degrees Celsius / hr. As described above, when crystal grains are grown at such a low heating rate, an unfavorable orientation is developed for the magnetic properties, so that the magnetic flux density is lower than when crystal grains are grown at a high heating rate. . However, in the motor core using the non-oriented electrical steel sheet according to the present embodiment, it is possible to suppress this decrease in magnetic flux density. Depending on conditions, the magnetic flux density may increase. Regarding the heating rate of the strain relief annealing that can enjoy the characteristics for the split core, the upper limit is 500 ° C./hr or less in consideration of the ability of the strain relief annealing equipment. The lower limit is 30 ° C./hr or more in consideration of the production efficiency of strain relief annealing. In addition, if the heating rate is approximately 50 ° C./hr to 200 ° C./hr, in which the motor core is generally subjected to strain relief annealing, the merit of using the non-oriented electrical steel sheet according to the present embodiment is sufficiently exhibited. The

  Although it depends on the steel components and hot rolling conditions, the maximum temperature reached and the holding time at 750 ° C. or higher are intended to obtain an appropriate crystal grain size. When the maximum temperature reached is 750 ° C. or higher, or the holding time at 750 ° C. or higher is 0.5 hours or longer, crystal grain growth occurs and specific magnetic characteristics can be effectively obtained, and sufficient magnetic properties required for a motor core are obtained. Characteristics (especially low iron loss) are obtained. When the maximum temperature reached is 850 ° C. or lower, or the holding time at 750 ° C. or higher is 100 hours or less, crystal grain growth becomes appropriate, magnetic flux density is improved, and low iron loss can be achieved.

Therefore, in terms of avoiding deterioration of magnetic characteristics, the manufacturing method of the motor core according to the present embodiment is based on the above conditions (heating rate: 30 ° C./hr to 500 ° C./hr, maximum reached temperature: 750 ° C. to 850 ° C., It is preferable to perform a heat treatment of 750 ° C. or higher holding time: 0.5 hour to 100 hours.
By performing this heat treatment, unnecessary distortion is released from the motor core, and iron loss can be reduced. And since the motor core of this embodiment uses the non-oriented electrical steel sheet according to this embodiment, a high magnetic flux density is maintained even after heat treatment, and an excellent motor core is obtained.

From the above, the non-oriented electrical steel sheet according to the present embodiment is useful as a core material because of its excellent magnetic properties. The non-oriented electrical steel sheet according to the present embodiment is excellent in punching workability when applied to a motor core material. Moreover, the non-oriented electrical steel sheet according to the present embodiment has an advantage that the decrease in the magnetic flux density B _{50 and} the deterioration of the iron loss are suppressed even after punching into a desired shape and after performing strain relief annealing. Therefore, the non-oriented electrical steel sheet according to the present embodiment can sufficiently meet the urgent demand for high efficiency and miniaturization in the field of electrical equipment, and its industrial value is extremely high.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the idea described in the claims, and these naturally belong to the technical scope of the present invention. It is understood.

<Example 1>
The slab having the chemical composition shown in Table 1 is subjected to rough hot rolling so that the thickness becomes 40 mm. Then, finish hot rolling is performed at the temperature shown in Table 1. Further, the finish hot rolling is the strain amount σ1 applied to the steel plate in the first half of the rolling pass ”/“ strain amount σ2 applied to the steel plate in the second half ”(denoted as“ first half strain amount σ1 / second half strain amount σ2 ”), and surface The difference between the temperature Ts and the plate thickness center temperature Tc (denoted as Ts−Tc) is set to the value shown in Table 1. The steel sheet after finish hot rolling is cold rolled at the total rolling reduction shown in Table 1 (denoted as the total cold rolling rate). The plate thickness of the finish hot rolling is adjusted so that the plate thicknesses of the steel plates after the cold rolling according to the total cold rolling ratios shown in Table 1 are all 0.35 mm. The steel sheet after cold rolling is subjected to finish annealing at a soaking temperature shown in Table 1 (the soaking time is 30 sec for all) to obtain a steel plate.

About the surface layer and intermediate | middle layer of the obtained steel plate, it observes according to the above-mentioned method, and the accumulation degree (intermediate layer {223} <252>) of {223} <252> orientation in an intermediate | middle layer is measured. Further, the integration degree of {100} <001> orientation in the surface layer (surface layer {100} <001> (MI ₀₀₁ )) and the integration degree of {100} <011> orientation in the surface layer (surface layer {100} <011> (MI ₀₁₁ )) and MI ₀₀₁ / MI ₀₁₁ is calculated. The results are shown in Table 2.
The ratio of the magnetic flux density _{B 50} of the average rolling direction and the direction perpendicular to the rolling direction, and the magnetic flux density _{B 50} and the saturation magnetic flux density Bs _(B 50 / Bs), and measured for iron loss _{(W 10/400).} Further, the average crystal grain size (grain size) is measured according to the method described above.

For the crystal grain size, the metal structure of the plate thickness cross section developed by corroding the grain boundary by nital etching was photographed with an optical microscope, and the line segment method for 100 or more crystal grains (a straight line was drawn on the metal structure photograph). And calculated from the number of intersections between the straight line and the grain boundary.
Moreover, about the material which made the soaking temperature of finish annealing comparatively low temperature among the obtained steel plates, the heating rate is 100 degreeC / hr, the maximum attainment temperature of 800 degreeC, and the holding time in 800 degreeC on the conditions for 2 hours. Then, strain relief annealing is performed, and changes in magnetic flux density (B _B / B _A ) due to additional heat treatment at a low heating rate are evaluated. The results are shown in Table 2.

  The punching accuracy is 20 mm in width by using a cylindrical mold (punch) with an outer diameter of 100 mm and an inner diameter of 80 mm, and a corresponding mold (die) with a punching clearance of 3/100 mm. The ring-shaped sample is punched out and evaluated by the difference between the maximum value and the minimum value of the outer diameter of the punched-out ring sample (denoted by punching accuracy [μm]).

Here, the average B ₅₀ in the rolling direction and the direction perpendicular to the rolling is obtained from the magnetic flux density when excited with a magnetizing force of 5000 A / m. Specifically, it is an average value obtained by measuring B ₅₀ in the direction along the rolling direction (0 °) and in the direction perpendicular to the direction along the rolling direction (90 °).
The average core loss in the rolling direction (0 °) and the direction perpendicular to the rolling direction (90 °), the average value when the same direction was measured with the direction of measurement of the average of the magnetic flux density B ₅₀ in the rolling direction and the direction perpendicular to the rolling direction _And measured as iron loss (W _10/400 ) under the conditions of maximum magnetic flux density of 1.0 T and frequency of 400 Hz.
In the table, B _B represents the magnetic flux density after SRA, and B _A represents the magnetic flux density before SRA.

The invention example corresponding to the non-oriented electrical steel sheet of the present embodiment has an average magnetic flux density B ₅₀ , magnetic flux in the rolling direction and the direction perpendicular to the rolling, as compared with a comparative example that is outside the range of the non-oriented electrical steel sheet of the present embodiment. It can be seen that the change in magnetic flux density due to the ratio of density B ₅₀ to saturation magnetic flux density Bs (B ₅₀ / Bs), iron loss (W _10/400 ), and strain relief annealing (SRA) shows good results.

  11 Punching member, 13 Laminated body, 15 Teeth part, 17 Yoke part, 100 Motor core

Claims (8)

% By mass
C: 0.0030% or less,
Si: 0.01% to 3.50%
Al: 0.001% to 2.500%
Mn: 0.01% to 3.00%,
P: 0.180% or less,
S: 0.0030% or less, and the balance: chemical composition containing Fe and impurities,
A non-oriented electrical steel sheet having a degree of integration of {223} <252> orientations of 6 or less in an intermediate layer having a thickness of 1/10 to 1/5.   The non-oriented electrical steel sheet according to claim 1, wherein the degree of integration of {100} <001> orientations in the surface layer from the steel sheet surface to the plate thickness 1/10 is 6 or more. In the surface layer, the ratio between the integration degree of {100} <001> orientation (MI ₀₀₁ ) and the integration degree of {100} <011> orientation (MI ₀₁₁ ) is
MI ₀₀₁ / MI ₀₁₁ > 1.0
The non-oriented electrical steel sheet according to claim 1 or 2, satisfying the relationship: The ratio between the rolling direction and the direction perpendicular to the rolling direction of an average of the magnetic flux density _{B 50} in the case of excitation in the magnetizing force 5000A / m and saturation magnetic flux density Bs _(B 50 / Bs) is of claims 1 to 3 is 0.890 or more The non-oriented electrical steel sheet according to any one of the above. Steel plate after heat treatment was performed under the conditions that the magnetic flux density of the steel plate before heat treatment was B _A , the heating rate was 100 ° C./hr, the maximum temperature reached 800 ° C., and the holding time at 800 ° C. was 2 hours. when the magnetic flux density was _{B B,} the ratio _{B B} and the _{B a is,} B B / _{B a} ≧ 0.980 is satisfied a relationship of claims 1 to 4 any one-free according Oriented electrical steel sheet. A hot rolling step of hot rolling a slab having the chemical composition according to claim 1;
A cold rolling step for cold rolling to the steel plate after the hot rolling step;
A finish annealing step for finish annealing the steel sheet after the cold rolling step;
The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 5, wherein in the hot rolling step, at least one of the following conditions (a) and (b) is satisfied.
(A) Finishing hot rolling is started by setting the difference between the surface temperature Ts of the steel sheet and the center thickness Tc of the sheet to 50 ° C. or more. (B) (Strain amount σ1 applied to the steel sheet in the first half of the pass) / (In the second half of the pass) The finish rolling is continuously performed for a plurality of passes so as to satisfy the condition of the strain amount σ2) ≧ 1.5 applied to the steel plate.   The motor core which laminated | stacked the non-oriented electrical steel sheet of any one of Claims 1-5. A process of punching the non-oriented electrical steel sheet according to any one of claims 1 to 5 to obtain a punched member;
Laminating the punched member;
A method for manufacturing a motor core.